On buffetting control surfaces, when the local shock gets on the hinge line, the surface will buffet. I've seen this on Tristar spoilers a lot.. about .85 Mach, the local shock wanders around on top of the wing where the spoilers hinge, and these do a little dance.
With the X-1, the elevators lost effectiveness when the local shock was on the hinge line. Moving the whole horizontal was found to permit control. This was a SECRET for a long time, publicly debuting on the F-100 and then the MiG-19, the C-model of which showed up with a flying slab after the conventional version proved poor to lethal.